1. Field in the Industry
The present invention concerns a high hardness stainless steel for screws used in magnetic memory devices. More specifically, the invention concerns a high hardness stainless steel for screws which are used for fastening parts of magnetic memory devices, such as HDD (hard disk drive), made of a stainless steel.
2. Prior Art
In general, when parts of devices are combined and fastened with screws to set up the device, if hardness of the male screw and the female part are of the same level, then seizure of the tightly fastened threads may occur. When the seized screw is loosened at repairing of the device metal powder will fall out, and sometimes the metal powder causes failure or mulfunction of precision devices.
Hard disk drives, which are one of the precision devices, may be troubled if the above mentioned metal powder comes into the device. Therefore, in the magnetic memory devices it is necessary to use screws of such high hardness that they may not be seized and may not cause metal powder releasing. Also, it is desired that the screws used for setting up magnetic memory devices are non-magnetic so that they may not adhere to tools during the setting up.
The screws conveniently used in the magnetic memory devices are those having grooves of various shapes at the head, and the female threads to engage the screws are made of aluminum. Thus, the material for the screws have been stainless steel wires having a hardness higher than that of aluminum such as SUS XM7 (containing C: up to 0.08%, Si: up to 1.00%, Mn: up to 2.00%, Ni: 8.50-10.50%, Cr: 17.00-19.00% and Cu: 3.00-4.00% and the balance of Fe).
It is today""s tendency to change the material of parts of the magnetic memory devices, in order to follow increasing memory capacity, from aluminum to stainless steels such as SUS 430 (containing C: up to 0.12%, Si: up to 0.75%, Mn: up to 1.00%, Cr: 16.00-18.00% and the balance of Fe) or equivalent steels. Then, the screws made of conventionally used SUS MX7 may cause, due to the small difference in hardness, seizure at fastening and may result in failure and mulfunction of the devices.
The object of the present invention is to provide a non-magnetic high hardness stainless steel for screws to be used in the magnetic memory devices, the stainless steel having a hardness higher than those of stainless steels (SUS430 or steels equivalent thereto) used for constructing magnetic memory devices and conventional SUSXM7 steel, and exhibiting anti-seizure property better than that of the conventional SUSXM7 steel.
This object is achieved by the stainless steel according to the present invention.